Imagine walking into work tomorrow morning to find the following email: “To fully become a global company, effective immediately, our business language will be English. All verbal and written communication should be conducted in English only.” Full stop.

If you’re a native English speaker, you may be celebrating. If you’re a nonnative speaker, what’s your initial gut reaction? Try: “How am I going to do this every day?” “My colleagues speak English much better than I do.” “What’s going to happen to my career?” “I didn’t sign up for this.” “I feel stupid when I speak English.” Professionals expect to progress, not regress, at work. For most, discovering that their native language can no longer serve as a primary mode of communication would be, to say the least, disruptive. Such an event has become the reality for millions of employees around the world.

Of course, from a managerial perspective, unrestricted multilingualism — where verbal and written communications are generated in multiple languages — is inefficient. The proliferation of integrated organizational systems, the need to tightly coordinate work and to serve clients worldwide has accelerated the move towards the use of English as a lingua franca (common language) no matter where companies are headquartered. SAP and Siemens are based in Germany but have mandated English as their business language; Kone Elevators in Sweden has set English as its sole mode of business communication. Even Microsoft in Beijing has implemented English as its business language for its local Chinese employees. Indeed, the business case for the one global language policy is indisputable.

Yet I’ve been surprised at the extent to which leaders of multinational firms neglect a systematic implementation of these programs. I once asked a leader of a high-profile European multibillion dollar company how he went about preparing his employees for the English policy he set two years earlier. He stared at me for a few seconds and blurted, “We actually never talked about it.” Then: “We made the announcement and never brought it up again.”

Perhaps this is an extreme case, but according to my research, most leaders miss the ripple effects of a one global language policy. A recent study reported how Siemens unveiled its mandate. The CEO declared English as the official business language to promote cross-unit efficiency and renamed units to their English word equivalents, but did little else to socialize employees to the new rule.

Failing to follow through can have a significant impact on employee morale, professional identities, and overall productivity — and they decrease efficiency, which is ironic given their intent. Many nonnative speakers lose a great deal of latitude in their communication ability, and, by extension, their professional capacity. They fear being viewed as incompetent. Some feverishly rehearse oral presentations before publicly presenting their arguments, or defer to the most fluent speakers when presenting in front of managers. As a result, they don’t bring themselves fully to their work.

In response, leaders need to publicly destigmatize language challenges. Granted many lingua franca companies do provide English and cross-cultural training, but those won’t allay workers’ fears about their daily work, sense of job security, and future career prospects. Instead, companies should institute a full-out campaign empowering nonnative speakers, and confirming that their contributions are valued and their capabilities are respected. They should take great care in creating an environment where employees can embrace the mandate with relative ease. After all, language is social, emotional, and intellectual, the source of identity and power and the most fundamental source of human interaction.

A one-language directive is likely the most important policy that multinationals can institute for their globalizing companies. But the policy is the beginning, not the end, of leadership challenges posed by global communication. Helping employees see the one English global language policy as an opportunity for personal growth rather than professional failure is the vital first step.

Tsedal Neeley is an Assistant Professor in the Organizational Behavior area at Harvard Business School.